JavaScript - Wait for execution

Question

I have the code below:

function foo() {
    setTimeout(function() {
        console.log("a");
    }, 0);
    console.log("b");
    console.log("c");
}

In my console, I have the result below:

b
c
undefined
a

I need get the result below:

undefined
a
b
c

The commands to print "b" and "c", need stay in the root foo function.

How to do it?

-

The case above simplifies my need.

No matter how short the timeout is, the function won't run until the script finishes and you return to the main event loop. — Barmar, Jun 10 '14 at 17:10
@j08691 setTimeout represents one ajax fucntion assync, and I need return (in main function) one boolean because, I using TypeScript and the return need stay in main function. — FabianoLothor, Jun 10 '14 at 17:13
@FabianoLothor You have to use the events and callbacks associated with an asynchronous task to control execution timing. The script simply doesn't execute strictly top-to-bottom when you involve anything asynchronous as they are very intentionally "*outside of the normal flow*." — Jonathan Lonowski, Jun 10 '14 at 17:17
@JonathanLonowski I know, the problem is: I using TypeScript and the language not compile when I put the return in callback function. You understand? — FabianoLothor, Jun 10 '14 at 17:20
@FabianoLothor Well, it's not possible to `return` the result of an asynchronous task. [How to return the response from an AJAX call?](http://stackoverflow.com/questions/14220321/how-to-return-the-response-from-an-ajax-call) You have to write your code in a different manner and TypeScript can handle callbacks and promises as well. — Jonathan Lonowski, Jun 10 '14 at 17:21
@FabianoLothor then you should update your question to state that you need to return a result from timeout — Andrew Vermie, Jun 10 '14 at 17:24
Read upon [What do I do if I want a JavaScript version of sleep()?](http://stackoverflow.com/q/951021/1048572) and [Why is my variable undefined after I modify it inside of a function? - Asynchronous code reference](http://stackoverflow.com/q/23667086/1048572). Not sure if I should close it as a duplicate. — Bergi, Jun 10 '14 at 17:27
@Ingmars: `undefined` is the return value of `foo()`, when that is evaluated from the console. — Bergi, Jun 10 '14 at 18:08

Monarch Wadia · Answer 1 · 2014-06-10T17:59:52.597

-2

function bar(){
    that = this;
    this.printed = undefined;

    this.foo = function() {
        if (typeof this.printed === "undefined") {

            this.printed = false;

            console.log("a");

            setTimeout(function() {
                that.printed = true;
                that.foo();
                return undefined;                
            }, 0);
        }


        if(this.printed == true) {
            console.log("b");
            console.log("c");
            this.printed = undefined;
        }
    }
}

new bar().foo()

edited Jun 10 '14 at 17:59

answered Jun 10 '14 at 17:19

Monarch Wadia

4,400
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No. Don't do that. This function cannot run in parallel to itself, and behaves erratic when one tries to. – Bergi Jun 10 '14 at 17:30
@Bergi OP never asked for multiple instances to be run. – Monarch Wadia Jun 10 '14 at 17:31
1

That's one of the implicit features of an asynchronous function. OK, sometimes one might want to *lock*, but not like this. "Recursively" calling itself when there is no recursion required is confusing and should be avoided. – Bergi Jun 10 '14 at 17:36
The output is as follows for me: `Unhandled Error: 'this.foo' is not a function` - even worse. Apart from that, making `foo` a method and `printed` a non-global property still doesn't solve problem. I'm not sure why you deleted your first answer, it was fine! – Bergi Jun 10 '14 at 17:47
Fixed! Please check again, the output is proper for me, and it now handles multiple parallel calls as well. – Monarch Wadia Jun 10 '14 at 18:01
no. Apart from [`that` being global](http://blog.niftysnippets.org/2008/03/horror-of-implicit-globals.html), `var x=new bar(); x.foo(); x.foo();` still does not work. – Bergi Jun 10 '14 at 18:06

JavaScript - Wait for execution

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